(1) Field of the Invention
This invention relates to an input method and apparatus for an input unit in a programmable controller, and more particularly to a dynamic input method and apparatus for a programmable controller.
(2) Description of Prior Art
A programmable controller extensively employed for the high-precision sequence control of variety of a devices, apparatuses or systems often operates according to the dynamic input method in which a number of input data applied thereto are divided into a plurality of parts, which are successively loaded with switching means.
FIG. 1 is a block diagram showing one example of an input unit and a control section in a programmable controller employing a conventional dynamic input method.
In FIG. 1, reference numeral 1 designates an input circuit section for receiving input signals, which has a number of input terminals (not shown). The input terminals are divided into groups (blocks) each including, for instance, eight (8) input terminals, so that the input circuit section 1 receives the input signals separately according to the groups specified by a group specifying signal applied separately thereto. Hereinafter, for simplification in description, the term "group (block)" will be referred to as "block", when applicable. The group specifying signal will be referred to as "a block painter signal".
Further in FIG. 1, reference numeral 2 designates an input data latch section comprising latch means 21 through 24, for temporarily holding input data; 3, an oscillator; 4, a frequency divider comprising for instance a counter for frequency-dividing the output pulse of the oscillator 3; 5, a decoder for converting the output of the frequency divider 4 into a block pointer signal; and 10, a control section for controlling the programmable controller in its entirety. The control section 10 comprises a CPU (central processing unit); memory for storing programs, and data (both not shown). The control section 10, being generally independent of the above-described input unit, is connected to the input data latch section 2 forming the input unit through a data transmitting, signal line A.
In operation of the circuit shown in FIG. 1, the output pulse signal of the oscillator 3 is applied to the frequency divider 4 where it is subjected to frequency division. The pulse signal thus frequency-divided; that is, the output of the frequency divider 4 is applied to the decoder where it is converted into a block pointer signal. The block pointer signal is applied to the input circuit section 1, so that the latter 1 receives the input data at the block thus specified and outputs it. At the same time, the block pointer signal is further applied to the latch means (21 for instance) in the input data latch section 2, which corresponds to the specification of block, so that the input data received by the input circuit section 1 is latched by the latch means 21. The decoder 5 outputs for instance, first, second, third and fourth block pointer signals repeatedly in the stated order. In response to the block pointer signals, the corresponding input data are successively received by the input circuit 1 and then latched by the corresponding latch means 21 through 24, so that the latest data are stored therein at all times. The control section 10 receives the input data from the input data latch section 2 when necessary.
The above-described input data latch section 2 is indispensable in the programmable controller operating according to the conventional dynamic input method, in which, in loading the input data from the input circuit 1 into the control section 10, they are temporarily latched in the input data latch section 2. Accordingly, it is disadvantageous in that the number of circuit elements constituting the latch section is relatively large resulting in having difficulties in suitably arranging those circuit elements on the printed circuit board and accordingly wiring them. Consequently, the programmable controller is expensive.